1. Field Of The Invention
The present invention relates generally to optical polarization transformation, and particularly to optical polarization rotators, and most particularly to electrically tunable azimuth optical rotators for rotating the polarization state of polarized light beam.
2. Technical Background
Transformation of the state of polarization (SoP) of light beams is important in many applications. Polarization transformer converts the SoP of an input light beam to a predetermined output SoP. Polarization transformers can convert any input SoP to any output SoP, which means a linearly polarized light could be converted to an elliptical one. A polarization rotator is a narrower type of a polarization transformer in that the rotator can only rotate the polarization direction. Polarization rotators, such as azimuth rotators are known, in which the rotation of the SoP on the Poincare sphere (PS) is about an axis that intercepts with the north and the south poles. This known azimuth rotator will preserve the polarization property of the light beam while rotating the polarization. Hence, a linearly polarized beam will be still linearly polarized after the rotation. For example, the circularly or elliptically polarized light will each retain their original respective polarizations.
Rotators are basic elements that are employed in a variety of fiber optic devices. The simplest way to do this is with a birefringent half-wave plate to rotate the input light beam by a predetermined angle. The limitation of this approach is that the rotation angle is preset and not changeable. There are demands on tunable azimuth rotators in various applications including dynamic gain flattening filters (DGFF), polarization mode dispersion (PMD) emulators, PMD compensators that include a variable digital group delay (VDGD) line, and other optical telecommunication applications. Such applications often require cost-effective space-efficient high-speed low-loss tunable rotators that can efficiently rotate the arbitrary polarization state of a light beam by any demanding angle.
There are several known approaches that can achieve the azimuth rotation. Known azimuth rotators include different types made from liquid crystal, electro-optical (E-O) materials, magneto-optical materials, and mechanical movement of birefringent fibers. However, these known approaches do not have the high-speed response, low insertion loss or small size required of advance optical components and systems. For example, a magneto-optical based rotator requires a magnetic field, so it is inconvenient in most applications and difficult to integrate into optical systems. A liquid crystal based rotator tends to be slow in response. Mechanical movements may cause various kinds of errors and is also slow in response. The electro-optical rotators, mostly based on LiNbO3 waveguide, are high in optical insertion loss.
Hence, a need exists in the art for a cost-effective space-efficient high-speed tunable rotator that can perform an azimuth rotation on an arbitrary polarized light beam.
One aspect of the invention is the use of an electric voltage controlled ferro-electric variable phase retarder to form an electrically controllable azimuth optical rotator.
In another aspect, the present invention includes the ferro-electric materials, such as PLZT, PMN-PT, and PZN-PT to form the electric voltage controlled ferro-electric variable phase retarder.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operations of the invention.